<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>2_原生事件绑定</title>
</head>
<body>
  <button id="btn1">按钮1</button>
  <button id="btn2">按钮2</button>
  <button onclick="demo()">按钮3</button>
</body>
<script>
  const btn1 = document.getElementById("btn1")
  btn1.addEventListener("click", function() {
    alert("按钮1被点击了")
  });

  const btn2 = document.getElementById("btn2")
  btn2.onclick = function() {
    alert("按钮2被点击了")
  };

  function demo() {
    alert("按钮3被点击了")
  }
</script>
</html>